Fuel Pump

ABSTRACT

A fuel pump is obtained, by which a high fuel pump-up height and a short fuel pump-up time can be achieved without deteriorating a fuel injection state by discharging a vapor toward the [Means for Resolution]  
     An air exhaust port having a channel area s satisfying s≧0.07 mm 2  is provided in a lower channel including the terminal of a pump channel, and an air exhaust valve mechanism that opens the valve when the pump is started to exhaust intake air and closes the valve as soon as the application of pressure on the fuel is started to prevent the fuel from being exhausted to the outside of the pump channel is provided. Also, a vapor exhaust port is provided in the pump channel between the air exhaust port and the inlet portion of the pump channel, and a vapor exhaust valve mechanism that closes the valve when the pump is started to prevent a negative pressure at the fuel intake port from dropping and opens the valve when application of pressure on the fuel is started to exhaust fuel containing a vapor to the outside of the pump channel is provided.

TECHNICAL FIELD

The present invention relates to a fuel pump that pumps up fuel from a fuel tank by rotating an impeller comprising a rotator, and more particularly, to a fuel pump capable of not only improving the fuel intake performance but also exhausting a gas, such as a vapor, from a pump channel.

BACKGROUND ART

A fuel pump in the related art of this type is disclosed in JP-A-11-218059. In the fuel pump in the related art, a pump channel is formed along the periphery of the impeller, and a pressure is applied to the fuel in the pump channel by rotating the impeller. The fuel pump in the related art is provided with a gas exhaust port having a diameter d satisfying 0.2 mm≦d≦0.9 mm on the side closer to the rotation direction of the impeller than half the pump channel length, for example, at the terminal of the pump channel, for a vapor to be exhausted promptly through the gas exhaust port in a state where a fuel pressure in the pump channel is low, that is, during low-speed rotations of the pump. Further, a valve mechanism is provided to the gas exhaust port, by which the gas exhaust port is closed when a fuel pressure in the pump channel reaches or exceeds a specific pressure for a vapor generated in the pump channel together with the fuel to be discharged toward the engine.

Patent Document 1: JP-A-11-218059, in particular, page 2, line 28 on the right column through page 3, line 20 on the left column.

DISCLOSURE OF THE INVENTION PROBLEMS THAT THE INVENTION IS TO SOLVE

Because the fuel pump in the related art leaves the gas exhaust port open until the fuel pressure in the pump channel reaches or exceeds the specific pressure, there arises a problem that an exhaust of the fuel through the gas exhaust port cannot be avoided and a fuel discharge rate is reduced. Also, there is another problem that a vapor generated when the fuel pressure in the pump channel reaches or exceeds the specific pressure is discharged toward the engine together with the fuel because the gas exhaust port has been closed by the valve mechanism. This may possibly give rise to an error in a fuel injection rate of the injector.

The invention was devised to solve the problems as discussed above, and therefore has an object to obtain a fuel pump capable of not only preventing a reduction of a fuel discharge rate as well as a discharge of a vapor toward the engine during low-speed rotations of the pump, but also improving the fuel intake performance.

MEANS FOR SOLVING THE PROBLEMS

A fuel pump of the invention is a fuel pump having a pump channel formed around a rotator from an inlet portion to a terminal portion, which pumps up fuel through a fuel intake port communicating with the inlet portion using rotations of the rotator and applies a pressure to the fuel in the pump channel, and the fuel pump is characterized in that: an air exhaust port is formed in a lower channel including the terminal portion of the pump channel while a vapor exhaust port is formed in the pump channel between the air exhaust port and the inlet portion, and an air exhaust valve mechanism that prevents the fuel from being exhausted through the air exhaust port is provided to the air exhaust port while a vapor exhaust valve mechanism that prevents air from being taken in through the vapor exhaust port is provided to the vapor exhaust port; and when a pressure is applied to the fuel in the pump channel, the air exhaust valve mechanism is shifted to a valve-close state from a valve-open state and the vapor exhaust valve mechanism is shifted to a valve-open state from a valve-close state.

ADVANTAGES OF THE INVENTION

In the fuel pump of the invention, because the air exhaust port is formed in the lower channel including the terminal portion of the pump channel, it is possible to use a long pump channel from the inlet portion to the terminal portion of the pump channel as the pressure channel. Also, because the vapor exhaust valve mechanism is kept in the valve-close state until a pressure is applied to the fuel in the pump channel, the fuel can be pumped up by using effectively the long pump channel extending from the inlet portion to the terminal portion. It is thus possible to improve the fuel intake performance by increasing a negative pressure at the fuel intake port.

BEST MODE FOR CARRYING OUT THE INVENTION FIRST EMBODIMENT

FIG. 1 is a cross section showing a first embodiment of a fuel pump of the invention. FIG. 2 is a cross section taken along the line A-A of FIG. 1 to show a casing cover in the first embodiment. FIG. 3 is a cross section taken along the line B-B of FIG. 2 to show an air exhaust port portion in the first embodiment. FIG. 4 is a cross section taken along the line C-C of FIG. 2 to show a vapor exhaust port portion in the first embodiment. FIG. 5 through FIG. 7 are characteristic views. FIG. 5 shows a measurement result of the fuel intake performance and that of a comparative example to make the advantage of the first embodiment clear. FIG. 6 and FIG. 7 show results of trial computations using a flow rate computational expression on a nozzle type Venturi meter. FIG. 6 shows a hole diameter of the air exhaust port and a pressure loss caused by passing of air. FIG. 7 shows a hole diameter of the air exhaust port and an exhaust flow rate of fuel.

Referring to FIG. 1, a fuel pump 10 is used in a fuel supply system, for example, in a vehicle. To be more concrete, the fuel pump 10 is accommodated in the fuel tank of an unillustrated vehicle, and it supplies fuel taken in from the fuel tank to the engine E. The fuel pump 10 comprises a pump portion 20 and a motor portion 30 that drives the pump portion 20. The motor portion 30 constitutes an electromagnetic driving portion for the pump portion 20. The motor portion 30 is a direct-current motor equipped with a brush, and is formed by disposing an unillustrated permanent magnet annularly within a cylindrical housing 11 and disposing an armature 32 concentrically on the inner periphery of the permanent magnet. Meanwhile, the pump portion 20 comprises a casing main body 21, a casing cover 22, and an impeller 24 comprising a rotator. Because the pump portion 20 is the gist of the invention, the pump portion 20 will be described in detail below.

The casing main body 21 and the casing cover 22 are formed, for example, by means of die cast molding of aluminum, and the casing main body 21 and the casing cover 22 together form a single casing member 200. The impeller 24 is accommodated in the interior of the casing member 200 to be free to rotate. The casing main body 21 is press-fit immovably on the inner side at one end of the housing 11. The casing cover 22 is fixed oppositely to the casing main body 21 by means of caulking or the like at one end of the housing 11 to cover the casing main body 21. A bearing 25 is fit in the casing main body 21 at the center, and a thrust bearing 26 is press-fit immovably in the casing cover 22 at the center. One end of a rotating shaft 35 of the armature 32 is supported on the bearing 25 to be free to rotate in the radial direction. A load of the rotating shaft 35 in the thrust direction is supported on the thrust bearing 26. The other end of the rotating shaft 35 is supported on a bearing 27 to be free to rotate in the radial direction.

A fuel intake port 40 is formed in the casing cover 22. It is known that fuel 100 within the fuel tank is taken into a pump channel 41 through the fuel intake port 40 bypassing through an intake filter 101 and an intake pipe 102 in association with rotations of the impeller 24 that is provided with blades on the peripheral portion. The pump channel 41 is formed between the casing main body 21 and the casing cover 22 along the outer periphery of the impeller 24 almost in the shape of a capital C. It is also known that a pressure is applied to the fuel (no reference numeral is labeled to be distinguished from the fuel 100 within the fuel tank, and the same applies in the following descriptions) taken into the pump channel 41 by rotations of the impeller 24, so that it is pumped into a fuel chamber 31 in the motor portion 30.

The casing cover 22 will now be described in detail. Referring to FIG. 2, a C-shaped fuel groove 23 is formed in the surface opposing the casing main body 21 (see FIG. 1). The fuel groove 23 defines a groove channel 50. Also, the casing main body 21 is provided with a groove channel 50 a that opposes the groove channel 50, and these groove channels 50 and 50 a define the pump channel 41 in the interior of the casing member 200. The groove channel 50 comprises an inlet portion 51 that communicates with the fuel intake port 40, an introduction channel portion 52 whose channel width becomes narrower and whose channel depth becomes shallower gradually from the inlet portion 51, and a pressure channel portion 53 formed from the introduction channel portion 52 toward a terminal portion 54 of the groove channel 50. Referring to FIG. 2, a rotation direction of the impeller 24 comprising a rotator is indicated by an arrow N. The groove channel 50 is formed to extend along the rotation direction N from the inlet portion 51 up to the terminal portion 54.

The groove channel 50 is provided with an air exhaust port 110 and a vapor exhaust port 120. The air exhaust port 110 and the vapor exhaust port 120 independently penetrate through the casing cover 22 so that the pump cannel 41 communicates with the interior of the fuel tank installed outside the fuel pump 10 (see FIG. 1). The air exhaust port 110 is formed in the terminal portion 54 of the groove channel 50. The vapor exhaust-port 120 is formed between the inlet portion 51 and the air exhaust port 110 at a position spaced apart from the air exhaust port 110 by a specific distance on the rotation side inverse to the rotation direction N. The air exhaust port 110 is furnished with a function of exhausting air present within the pump channel 41 and the intake pipe 102 (see FIG. 1) to the fuel tank when the pump is started. The vapor exhaust port 120 is furnished with a function of exhausting air bubbles containing a vapor as a fuel steam generated in the pump channel 41 (hereinafter, referred to as the vapor) to the fuel tank.

The exhaust ports 110 and 120 will now be described. Referring to FIG. 3, an air exhaust valve mechanism 111 comprising a valve seat member 112 fixed to the casing cover 22, a valve member 113, and a spring 114 is provided on the outlet end of the air exhaust port 110, that is, below the air exhaust port 110 of FIG. 3. The valve seat member 112 is molded, for example, from resin, and a through-hole 115 serving as an air channel is formed at the center. The diameter of the through-hole 115 is set larger than the diameter of the air exhaust port 110. Meanwhile, spring seats 116 a and 116 b are provided to the valve member 113 and the casing cover 22, respectively. The spring 114, which is set to have a free length to prevent the valve member 113 from seating on the valve seat member 112, is fit in both the spring seats 116 a and 116 b.

Referring to FIG. 4, a vapor exhaust valve mechanism 121 comprising a valve seat 122 formed in the casing cover 22, a valve member 123, a spring pressing member 124, and a spring 125 is formed at the outlet end of the vapor exhaust port 120, that is, below the vapor exhaust port 120 of FIG. 4. The spring pressing member 124 is molded, for example, from resin, and a through-hole 126 serving as a vapor channel is formed at the center. The diameter of the through-hole 126 is set larger than the diameter of the vapor exhaust port 120. Meanwhile, spring seats 127 a and 127 b are provided to the spring pressing member 124 and the valve member 123, respectively. The spring 125 that pushes the valve member 123 in a direction for the valve member 123 to seat on the valve seat 122 is fit in both the spring seats 127 a and 127 b.

Operations of the fuel pump 10 will now be described in the light of the configuration as has been described. As is shown in FIG. 1, the armature 32 starts to rotate as power is supplied to a coil (no reference numeral is labeled) wound around the outer periphery of a core 32 a of the armature 32 from an unillustrated power supply via a terminal 46 buried in a connector 45, an unillustrated brush, and a commutator 34 provided at the top of the armature 32 accommodated in the motor portion 30 to be free to rotate, which causes the rotating shaft 35 to rotate. The impeller 24 then starts to rotate in association with rotations of the rotating shaft 35.

When the impeller 24 starts to rotate, air present inside the pump channel 41 receives kinetic energy from the respective blades of the impeller 24, and the pressure rises inside the pump channel 41. In this instance, the air exhaust valve mechanism 111 (see FIG. 3) is in a valve-open state, that is, the air exhaust port 110 is in an open state toward the fuel tank, whereas the vapor exhaust valve mechanism 121 (see FIG. 4) is in a valve-close state, that is, the vapor exhaust port 120 is in a close state toward the fuel tank. Pressure-raised air is thus exhausted through the air exhaust port 110 (see FIG. 2) alone. A negative pressure is generated in the vicinity of the fuel intake port 40 as the pressure-raised air is exhausted, and air inside the intake pipe 102 connected to the fuel intake port 40 is also drawn into the pump channel 41. Consequently, the fuel 100 within the fuel tank is pumped into the pump channel 41 through the fuel intake port 40 via the intake pipe 102, and the pressure of the fuel rises inside the pump channel 41 as it receives kinetic energy from the respective blades of the impeller 24 in the same manner as above.

As soon as the pressure of the fuel starts to rise inside the pump channel 41, the air exhaust valve mechanism 111 of FIG. 3 shifts to the valve-close state from the valve-open state, while the vapor exhaust valve mechanism 121 of FIG. 4 shifts to the valve-open state from the valve-close state. To be more concrete, with a load that is increasing due to a difference of specific gravities between air and fuel, the valve member 113 of the air exhaust valve mechanism 111 closes the through-hole 115 as it seats on the valve seat member 112 against a contractive force of the spring 114. Also, the valve member 123 of the vapor exhaust valve mechanism 121 opens the vapor exhaust port 120 as it moves away from the valve seat 122 against a pushing force of the spring 125. Any further exhaust of fuel through the air exhaust port 110 can be suppressed by closing the air exhaust port 110, and a vapor generated under a high fuel pressure state is exhausted to the fuel tank by opening the vapor exhaust port 120. The fuel with its pressure being raised inside the pump channel 41 is pumped into the fuel chamber 31 shown in FIG. 1, after which it passes by the periphery of the armature 32 and is discharged toward the engine E through a fuel discharge port 43. As is shown in FIG. 1, a check valve 44 is accommodated in the fuel discharge port 43, and a satisfactory starting property of the engine is achieved, for example, by maintaining the pressure in the tube up to the engine E by means of the check valve 44 while the engine E is stopped.

By setting the spring constants of the springs 114 and 125 in such a manner that the air exhaust valve mechanism 111 in the valve-open state shifts to the valve-close state and the vapor exhaust valve mechanism 121 in the valve-close state shifts to the valve-open state at the timing at which the pressure of the fuel starts to rise as has been described, it is possible to prevent the fuel from flowing out by keeping the air exhaust port 110 closed while the pressure is applied to the fuel including a period of the low-speed rotations of the pump. A fuel discharge rate is therefore not reduced. Subsequently, while the pressure is applied to the fuel, a discharge of a generated vapor toward the engine E is prevented by keeping the vapor exhaust port 120 open. It is thus possible to achieve an advantage that an exact fuel injection rate of the injector can be maintained. Also, in addition to this advantage, because the vapor exhaust port 120 is kept closed until the pressure of the fuel rises, not only is it possible to prevent a drop of the negative pressure at the fuel intake port 40, but it is also possible to use almost the entire channel from the fuel intake port 40 to the air exhaust port 110 in the pump channel 41 that makes almost a full circle within the casing member 200 as a relatively long pressure channel. A negative pressure at the fuel intake port 40 can be thus increased markedly. When the negative pressure is increased, it is possible to increase a fuel pump-up height (a dimension h from the fuel liquid surface to the fuel intake port 40 shown in FIG. 1), which is one of indications indicating the improvement of the performance of the fuel pump 10. A degree of freedom can be therefore expected to increase, in particular, for the layout design including the fuel tank.

In order to confirm the improvement of the fuel pump-up height, that is, that the fuel intake performance of the first embodiment, the measurement result together with that of a comparative example will be described with reference to FIG. 5(a). FIG. 5(a) shows a fuel pump-up characteristic F1 of the first embodiment and a fuel pump-up characteristic F2 of the comparative example by using the abscissa for a fuel pump-up time (sec) and the ordinate for the fuel pump-up height (mm). The measurement of the comparative example was performed while the air exhaust port 110 was kept closed and the vapor exhaust port 120 was kept open. To be more specific, in contrast to the first embodiment in which the almost the entire pump channel 41 from the fuel intake port 40 to the air exhaust port 110 is used as the pressure channel as has been described, the pressure channel of the comparative example that starts from the fuel intake port 40 and ends at the vapor exhaust port 120 is shorter. When the fuel pump-up characteristics F1 and F2 are compared with each other, for example, given four sec as the fuel pump-up time, then the fuel pump-up height of the first embodiment is about twice that of the comparative example. In the fuel pump-up characteristic F1, the fuel intake performance, that is, a ratio of the fuel pump-up time with respect to the fuel pump-up height, is improved from the lower right (that is, the height is low for a long time) to the upper left (that is, the height is high for a short time) of the graph. It is therefore understood that the fuel intake performance is higher in the first embodiment than in the comparative example. FIG. 5(b) shows a pump chamber pressure characteristic P1 in the first embodiment and a pump chamber pressure characteristic P2 in the comparative example by using the abscissa for the length of the pressure channel in the pump channel 41 and the ordinate for an internal pressure of the pump chamber inside the pump channel 41. Arrows Pa, Pb, and Pc indicate the position of the fuel intake port 40, the position of the vapor exhaust port 120, and the position of the air exhaust port 110, respectively. At the position of the abscissa of FIG. 5(b), the internal pressure of the pump chamber on the ordinate is ambient pressure Pat. With the internal pressure of the pump chamber, the negative pressure is increased downward from the abscissa. The negative pressure at the position Pa of the fuel intake port 40 is a negative pressure Pn1 in the first embodiment whereas it is a negative pressure Pn2 in the comparative example, and the negative pressure Pn1 is larger than the negative pressure Pn2. To succeed in improving the fuel intake performance in the first embodiment is equal to obtain the pump chamber pressure characteristic P1 showing that the negative pressure at the starting point of the pressure channel, that is, at the fuel intake port 40 in the case of the first embodiment, increases with increasing lengths of the pressure channel.

As has been described, in order to improve the fuel intake performance, it is essentially necessary to ensure a sufficient pressure channel, and to this end, valve-closing by the air exhaust valve mechanism 111 and valve-opening by the vapor exhaust valve mechanism 121 are performed almost simultaneously in the first embodiment. Further, it is more preferable to set the spring constants of the both springs 114 and 125 in such a manner that the air exhaust valve mechanism 111 shifts to the valve-close state from the valve-open state and then valve-opening by the vapor exhaust valve mechanism 121 is performed with a slightly delay to the extent that a discharge of the vapor toward the engine E does not give any influence to a fuel injection rate of the injector. Even when the air exhaust port 110 and the air exhaust valve mechanism 111 are provided in a lower channel on the lower stream side of the pump channel 41 serving as the pressure channel, the same functions can be achieved regardless of the installation locations as long as they are provided in a fuel channel on the upper stream side of the check valve 44. It should be noted, however, that an air volume to be exhausted is increased with an expanding space in which air between the terminal portion 54 of the pump channel 41 and the air exhaust port is stored, which extends the fuel pump-up time. Whether such an extension is allowable can be judged appropriately according to the position of the fuel pump within the fuel tank.

The air exhaust port 110 can be provided at any appropriate position; however, a hole diameter d (see FIG. 3) needs to be of a size that a pressure loss caused when air passes through the air exhaust port 110 will not raise any problem. FIG. 6 shows a pressure loss characteristic PL at the air exhaust port 110 by using the abscissa for a hole diameter (mm) of the air exhaust port 110 and the ordinate as a pressure loss (kPa) caused by passing of air. Referring to FIG. 6, a pressure loss caused by passing of air is almost 0 (kPa) when the hole diameter is 0.3 mm or larger. The hole diameter d of the air exhaust port 110 is therefore preferably 0.3 mm or larger. As a result, it is possible to reduce a resistance caused by exhausting air taken in when the pump is started to the fuel tank, which can in turn shorten the air exhaust time. A time needed since power feeding to the fuel pump started until the pressure of the fuel starts to rise, that is, the fuel pump-up time can be thus shortened. The air exhaust port 110 is, for example, of a circular shape. However, it does not have to be of a circular shape, and it can take on any shape as long as s≧0.07 mm² is satisfied, where s is a channel area converted from the hole diameter d.

The upper limit of the hole diameter d of the air exhaust port 110 has not been discussed. Generally, the upper limit takes a value equal to or smaller than a value obtained by converting the cross section of the pump channel 41 to the hole diameter d. However, by taking into account an event that the air exhaust valve mechanism 111 breaks and fails to close the valve, it is necessary to secure a fuel discharge rate toward the engine even when the fuel is exhausted through the air exhaust port 110 while the pressure is applied to the fuel in the pump channel 41. In other words, the hole diameter d of the air exhaust port 110 has to be set so that a flow rate of the fuel exhausted through the air exhaust port 110 does not exceed the original fuel discharge rate of the fuel pump. FIG. 7 shows a fuel exhaust characteristic FE of the air exhaust port 110 by using the abscissa for a pore size (mm) of the air exhaust port 110 and the ordinate for an exhaust flow rate (L/h) of the fuel. As is shown in FIG. 7, let 80 (L/h) be the original fuel discharge rate of the fuel pump, then given 1.0 (mm) as the hole diameter d of the air exhaust port 110, an exhaust flow rate of the fuel through the air exhaust port 110 is 80 (L/h) . A fuel discharge rate toward the engine is therefore almost 0. However, by setting the hole diameter d of the air exhaust port 110 to 0.8 (mm) or smaller, a flow rate of the fuel exhausted through the air exhaust port 110 is 80 (L/h) or smaller. It is thus possible to maintain a minimum necessary fuel supply to the engine.

SECOND EMBODIMENT

FIG. 8 is a cross section of an air exhaust port portion in a second embodiment of the fuel pump of the invention. FIG. 8 is a cross section of the second embodiment corresponding to FIG. 3 showing the air exhaust port portion of the first embodiment. The second embodiment is substantially the same as the first embodiment (FIG. 3) except that an air intake preventing valve mechanism 130 is additionally provided to the air exhaust port 110. The air intake preventing valve mechanism 130 will be therefore described chiefly.

Referring to FIG. 8, the air intake preventing mechanism 130 comprising an air intake preventing valve seat member 131 fixed to a valve seat member 112 and an air intake preventing valve member 132 in the shape of an umbrella is provided at the outlet end of the air exhaust valve mechanism 111, that is, below the air exhaust valve mechanism 111 in FIG. 8. The air intake preventing valve seat member 131 is molded, for example, from resin, and a valve member holding hole 133 for the air intake preventing valve member 132 to be inserted immovably, a channel portion 134 serving as an air exhaust channel, and a seal portion 135 that exerts a sealing function with the air intake preventing valve member 132 are formed at the center. Meanwhile, the air intake preventing valve member 132 is molded from an elastic member, such as rubber, and includes an umbrella portion 136 exerting a sealing function with the seal portion 135, an axis portion 137 that is inserted into the valve member holding hole 133, and a fall-off preventing portion 138 that prevents a fall-off from the valve member holding hole 133. In other words, as is shown in the drawing, once the fall-off preventing portion 138 penetrates through the valve member holding hole 133 immovably, the umbrella portion 136 adheres firmly to the seal portion 135, and the channel portion 134 is consequently closed. The air intake preventing valve seat member 131 may be formed integrally with the valve seat member 112.

Operations will now be described. Because the air exhaust valve mechanism 111 keeps the valve open when the pump is started, air inside the pump channel 41 reaches the air intake preventing valve mechanism 130 through the air exhaust port 110. A pressure produced when the air is exhausted readily push opens the umbrella portion 136. The air is consequently exhausted to the fuel tank via the channel portion 134 in the same manner as the first embodiment. The air intake preventing valve mechanism 130 therefore does not interfere with the air exhausting function furnished to the air exhaust valve mechanism 111.

Meanwhile, while the pump is stopped, air starts to flow toward the pump channel 41 by way of the air exhaust port 110 in a reversed manner when the pump is started, as the fuel within the intake pipe 102 (see FIG. 1) starts to drop to the height of the fuel liquid surface within the fuel tank due to its own weight. As is obvious from FIG. 3, in the first embodiment in which the intake air preventing valve mechanism 130 is not provided, air undesirably flows toward the pump channel 41 via the through-hole 115 and the air exhaust port 110 because the air exhaust valve mechanism 111 is opened while the pump is stopped. The fuel within the intake pipe 102 therefore drops to the fuel liquid surface. Hence, when the pump is started next time, the fuel pump 10 has to pump up the fuel to the fuel intake port 40 from the fuel liquid surface within the fuel tank. The pressure of the fuel therefore starts to rise with a delay for the time needed to pump-up the fuel.

In the second embodiment, because the air intake preventing valve member 132 closes the seal portion 135, air will not flow toward the pump channel 41 through the air exhaust port 110 even after the pump is stopped. Hence, the pump channel 41 and the intake pipe 102 are maintained in a state where their interiors are filled with the fuel. In other words, referring to FIG. 8, with the use of the umbrella-shaped air intake preventing valve member 132, air flows from top to bottom by push opening the umbrella portion 136, whereas air will not flow from bottom to top because the seal portion 135 is sealed with the umbrella portion 136. By adding the air intake preventing valve mechanism 130, because the pressure of the fuel starts to rise as soon as the pump is started again, improvements of the starting property of the engine can be expected while achieving all the advantages described in the first embodiment.

INDUSTRIAL APPLICABILITY

The fuel pump of the invention can be used in a fuel supply system of a vehicle, such as an automobile.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section showing a first embodiment of a fuel pump of the invention.

FIG. 2 is a cross section taken along the line A-A of FIG. 1 FIG. 3 is a cross section taken along the line B-B of FIG. 2.

FIG. 4 is a cross section taken along the line C-C of FIG. 2.

FIG. 5 is a characteristic view showing measurement results of the fuel intake performance in the first embodiment and a comparative example.

FIG. 6 is a characteristic view showing a hole diameter of an air exhaust port and a pressure loss caused by passing of air.

FIG. 7 is a characteristic view showing a hole diameter of the air exhaust port and an exhaust flow rate of fuel.

FIG. 8 is a cross section of an air exhaust port portion in a second embodiment of the fuel pump of the invention.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

-   10: fuel pump -   24: impeller -   40: fuel intake port -   41: pump channel -   54: terminal -   100: fuel -   110: air exhaust port -   111: air exhaust valve mechanism -   120: vapor exhaust port -   121: vapor exhaust valve mechanism -   130: air intake preventing valve mechanism 

1. A fuel pump having a pump channel formed around a rotator from an inlet portion to a terminal portion, which pumps up fuel through a fuel intake port communicating with the inlet portion using rotations of the rotator and applies a pressure to the fuel in the pump channel, the fuel pump being characterized in that: an air exhaust port is formed in a lower channel including the terminal portion of the pump channel while a vapor exhaust port is formed in the pump channel between the air exhaust port and the inlet portion, and an air exhaust valve mechanism that prevents the fuel from being exhausted through the air exhaust port is provided to the air exhaust port while a vapor exhaust valve mechanism that prevents air from being taken in through the vapor exhaust port is provided to the vapor exhaust port; and when a pressure is applied to the fuel in the pump channel, the air exhaust valve mechanism is shifted to a valve-close state from a valve-open state and the vapor exhaust valve mechanism is shifted to a valve-open state from a valve-close state.
 2. The fuel pump according to claim 1, wherein: the air exhaust port is formed at the terminal portion of the pump channel.
 3. The fuel pump according to claim 1, wherein: the air exhaust port is formed in a fuel channel on a lower stream side of the terminal portion of the pump channel.
 4. The fuel pump according to claim 1, wherein: the air exhaust valve mechanism is shifted to the valve-close state from the valve-open state and the vapor exhaust valve mechanism is shifted to the valve-open state from the valve-close state almost simultaneously.
 5. The fuel pump according to claim 1, wherein: the air exhaust valve mechanism is shifted to the valve-close state from the valve-open state and then the vapor exhaust valve mechanism is shifted to the valve-open state from the valve-close state with a slight delay.
 6. The fuel pump according to claim 1, wherein: a channel area s of the air exhaust port satisfies s≧0.07 mm².
 7. The fuel pump according to claim 1, wherein: an air intake preventing valve mechanism that prevents air from entering into the air exhaust port while the air exhaust valve mechanism is in the valve-open state is provided to the air exhaust valve mechanism. 